The present invention relates to a speed controlling method for an induction motor, and more particularly to a technique of vector control without a speed sensor which does not require a speed sensor mounted on a motor and makes it possible to obtain high torque starting from a zero speed range.
As a method of controlling the speed of an induction motor, a method of vector control without a speed sensor is conventionally known. FIG. 14 shows a configuration of its control system. Reference numeral 1 denotes an induction motor; 2 a power inverter for outputting an output voltage proportional to a voltage command value V1*; 3 a coordinate transformer for effecting the coordinate transformation of inverter output currents iu and iw and computing d-axis and q-axis currents id and iq; 4 a voltage computing unit for computing a value of a leak-impedance voltage drop of the motor on the basis of id, iq and an output frequency command value .omega.1*; 5 and 6 adders for adding the voltage drop value to induced-electromotive-force command values ed* and eq* and outputting d-axis and q-axis voltage command values Vd* and Vq*; 7 a phase reference generator for integrating .omega.1* and outputting a phase reference .theta.; 8 a coordinate transformer for outputting an inverter output voltage command value V1* (three phase) on the basis of Vd* and Vq*; 9 computing unit for outputting a slip-frequency computed value .omega.s1 on the basis of id and iq; 12 an adder for adding .omega.s1 to a speed command value .omega.r* and outputting .omega.1*; and 13 an electromotive-force computing unit for computing eq* on the basis of .omega.1*.
It should be noted that "Okuyama, et al.: "Simplified Vector Control System without Speed and Voltage Sensors--Effects of Setting Errors in Control Parameters and their Compensation" The Transactions of The Institute of Electrical Engineers of Japan, Vol. 110-D, No. 5, May, 1990, pp. 477-486 is known as a related document.